1. Field of the Invention
The present invention relates to a composition which comprises a mixture of water-soluble, amino-functional silicon compounds which are essentially free from alkoxy groups, water, optionally a low content of alcohol and optionally a content of acid. Such compositions moreover are free from solvents, water and alcohols being excluded from the amount of solvent.
2. Description of the Related Art
Amino silanes are known as water-soluble adhesion promoters. Water-based compositions with multi-functional organopolysiloxanes are also known as adhesion promoters, cf. EP 0 716 128 A2. In these systems, the reason for the improvement in the water-solubility is essentially attributed to the amino-functional groups.
A number of further fields of application for amino-functional silanes or siloxanes are:
The use in coating systems, in the field of corrosion protection, for biocidal treatment of surfaces, in the treatment of wood, in the preparation of electro-photographic toners, as a constituent in amino-silicone fluids (U.S. Pat. No. 5,077,421), as a constituent in epoxy resins [Chemical Abstracts (1991)xe2x80x94CA 114: 83579s] for the preparation of organically modified glasses (EP 0 223 987 A2), as an anticancer agent [Chemical Abstracts (1983)xe2x80x94CA 99: 133650c], for modification of glass surfaces and glass fiber surfaces in wastewater treatment for the treatment of pigments, as a constituent in catalysts and for the preparation thereof (U.S. Pat. No. 4,053,534) and as a flocculating agent, to mention only a few examples.
It is moreover known to employ amino-functional partly hydrolyzed alkoxy silane oligomers to reduce the formation of agglomerates in inorganic powders. U.S. Pat. No. 5,543,173 thus discloses that such formulations also comprise considerable amounts of alcohol, and moreover said silane oligomers can also liberate significant amounts of hydrolysis alcohol
Since amino silanes, such as, for example, aminopropyltriethoxysilane or aminopropyltrimethoxy-silane, are water-soluble, they allow a water-based application, for example in aqueous glass fiber sizes. Also, the formation of alcohols which occurs on hydrolysis also has an adverse effect. For example, on aqueous application of aminopropyltriethoxysilane, ethanol is formed as a hydrolysis product to the extent of about 62% of the weight of silane employed. As a combustible, water-soluble liquid, ethanol reduces the flash point of such application solutions, which in general necessitates the use of expensive, explosion-proof apparatuses.
Another disadvantage of alcohol-containing solutions is the fact that for ecological and work safety reasons, the solvent alcohol must be removed by sometimes very expensive industrial procedures.
Aminoalkoxysilanes can form a maximum of one silanetriol group per molecule upon hydrolysis. Silanols and other silanol functions can crosslink with one another or with other OH functions, for example with OH functions of a substrate or of dissolved, emulsified or suspended monomeric or polymeric substances. Such OH functions could be, for example, silanol functions on silic, glass, mineral, glass fiber or mineral fiber surfaces, OH functions on cellulose, leather, paper, wood and the like, and also OH functions on metal surfaces or metal oxide surfaces and also OH functions on the surface of plastics or polymers in formulations, for example emulsions or dispersions of naturally occurring substances or plastics. To achieve a higher crosslinking density and possibly associated therewith an improvement in the use properties, two silanetriol units per molecule, for example, would be desirable. Two silanetriol units per molecule are obtained on hydrolysis of bis(trialkoxysilylalkyl)amines. However, aqueous solutions of such compounds are not stable. They tend to gel and flocculate out and therefore are not capable of application.
It is an object of the present invention to provide a water-based composition which comprises (bis)trihydroxysilylalkyl)amines or siloxanes derived therefrom, has the lowest possible content of alcohol, furthermore is free from solvents, and comprises silicon compounds which are essentially free from alkoxy groups.
The object of the invention may be accomplished with a composition, which comprises a mixture of
(a) water-soluble, amino-functional silicon compounds which are essentially free from alkoxy groups represented by the formula (I) and (II):
xe2x80x83NH2[(CH2)2NH]x(CH2)3SiO1.5xe2x80x83xe2x80x83(I)
(SiO1.5)(CH2)3[NH(CH2)2]yNH[(CH2)2NH]x(CH2)3SiO1.5xe2x80x83xe2x80x83(II)
xe2x80x83wherein
x is 0, 1 or 2, and
y and z are each independently 0, 1 or 2, and
(b) water,
It has been found, surprisingly, that a low-viscosity, generally, largely storage-stable composition which comprises a mixture of water-soluble, amino-functional silicon compounds which are essentially free from alkoxy groups, water, optionally a low content of alcohol and optionally a content of acid is obtainable by mixing at least one amino silane of the general formula III:
NH2[(CH2)2NH]x(CH2)3Si(OR)3xe2x80x83xe2x80x83(III)
where
x is 0, 1 or 2, and R is a linear or branched alkyl group having 1 to 4 C atoms,
and/or condensation products thereof, and
at least one amino silane of the general formula IV:
(RO)3Si(CH2)3[NH(CH2)2]yNH[(CH2)2NH]z(CH2)3Si(OR)3xe2x80x83xe2x80x83(IV)
xe2x80x83where y and z are 0, 1 or 2 and are identical or different, and R is a linear or branched alkyl group having 1 to 4 C atoms,
and/or condensation products thereof,
adding water and optionally acid, carrying out hydrolysis and removing essentially all of the hydrolysis alcohol produced. Condensation products of amino silanes of the general formula III or IV are understood as meaning those dimeric, trimeric, tetrameric or higher oligomeric products which as a rule are obtainable by condensation and/or pre-hydrolysis of the particular monomers, alcohol being split off.
The inventive composition moreover is usually obtained in a liquid form which is easy to apply, and is generally essentially free from solvent. When the composition according to the invention is used, because of the silicon compounds of the general formulae I and II contained therein, a higher crosslinking density in the polymeric cured siloxane structure and a significant improvement in the mechanical, chemical and thermal properties of treated substances, for example composite materials, such as, for example, glass fiber- and mineral fiber-reinforced plastics, paints and coatings and polymers with a filler content, can be achieved.
The composition according to the invention can also suitably be diluted with water in any ratio, no additional hydrolysis alcohol being formed. Generally, the present composition is stable to storage in an outstanding manner for more than 12 months.
A more complete appreciation of the invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description.
The composition of the invention may contain alcohol, acid, or both alcohol and acid. The composition according to the invention preferably has a content of alcohol of less than 5% by weight, particularly preferably less than 1% by weight, especially preferably from 1 ppm by weight to 0.5% by weight. In particular, such a composition can comprise methanol and/or ethanol as the alcohol.
The composition according to the invention furthermore has a content of silicon compounds of less than 60% by weight, preferably less than 50% by weight, and the content of silicon compounds is particularly preferably 0.1 to 40% by weight, and especially preferably 0.5 to 40% by weight.
The weight ratio here of the silicon compounds of the general formula I and of the general formula II in a composition according to the invention is suitably I/IIxe2x89xa71, the general formulae I and II including the silanols and siloxanes in each case in equilibrium thereto, as will be readily appreciated by those skilled in the art. The weight ratio of silicon compounds of the general formula I and of the general formula II is preferably I:II=1 to 100:1 particularly preferably I:II=1.5 to 30:1, and especially preferably I:II 1.5 to 4.5:1.
To further improve the stability of a composition according to the invention, in particular the stability of dilute solutions or solutions which comprise a high content of compounds of the general formula II, so-called xe2x80x9cbis productsxe2x80x9d, the pH can be adjusted by addition of an organic or inorganic Brxc3x6nsted acid. Hydrogen chloride, nitric acid, sulfuric acid, formic acid, acetic acid and propionic acid, for example, can be used for this purpose.
The pH of a composition according to the invention can be in the range from 1 to 14. It is suitably at a value less than 11, preferably in the range from 4 to 9.
The present invention also relates to the process for the preparation of a composition which comprises a mixture of water-soluble amino-functional silicon compounds which are essentially free from alkoxy groups, water, optionally a content of alcohol and optionally a content or acid, which comprises mixing at least one amino silane of the general formula III:
NH2[(CH2)2NH]x(CH2)3Si(OR)3xe2x80x83xe2x80x83(III)
in which x is 0, or 2, and R is a linear or branched alkyl group having 1 to 4 C atoms,
and/or condensation products thereof,
and at least one amino silane of the general formula IV:
(RO)3Si(CH2)3[NH(CH2)2]yNH[(CH2)2NH]z(CH2)3Si(OR)3xe2x80x83xe2x80x83(IV)
xe2x80x83in which y and z are 0, 1 or 2 and are identical or different and R is a linear or branched alkyl group having 1 to 4 C atoms,
and/or condensation products thereof,
adding water and optionally acid, carrying out hydrolysis and essentially removing the hydrolysis alcohol.
It has been found that at a weight ratio of the starting materials of the formula III and IV of III/IV less than 1, gel formation or a very severe clouding occur, and as a result can counteract a particularly advantageous application
Starting materials of the general formula ill and of the general formula IV are suitably employed in the process according to the invention in a weight ratio of III/IV ofxe2x89xa71, preferably with a weight ratio of III:IV=1 to 100:1; particularly preferably with a weight ratio of III:IV=1.5 to 30:1, and especially preferably with a weight ratio of III:IV=1.5 to 4.5:1.
Water-based, alcohol-freexe2x80x94apart from residual amountsxe2x80x94solutions which comprise bis(trihydroxysilylalkyl)-amines or corresponding oligomeric or polymeric siloxanes of the general formula II are thus now also accessible. In the process according to the invention, amino silanes of the general formula III which are preferably employed include
H2N(CH2)3Si(OCH3)3 (AMMO),
H2N(CH2)3Si(OC2H5)3 (AMEO),
H2N(CH2)2NH(CH2)3Si(OCH3)3 (DAMO),
H2N(CH2)2NH(CH2)2NH(CH2)3Si(OCH3)3 (TRIAMO),
xe2x80x83and compounds according to formula IV which are preferably employed include
(H3CO)3Si(CH2)3NH(CH2)3Si(OCH3)3 (Bis-AMMO),
(H5C2O)3Si(CH2)3NH(CH2)3Si(OC2H5)3 (Bis-AMEO),
(H3CO)3Si(CH2)3NH(CH2)2NH(CH2)2NH(CH2)3Si(OCH3)3 (Bis-DAMO),
(H3CO)3Si(CH2)3NH(CH2)2NH(CH2)2NH(CH2)2NH(CH2)2NH(CH2)3Si(OCH3)3 (Bis-TRIAMO)
However, it is also possible to employ corresponding compounds with other alkoxy groups, and methoxy and ethoxy groups are preferred as hydrolyzable groups. Mixtures with in each case more than one of the compounds of the general formulae III and IV can furthermore employed.
The amino silanes of the general formula III can also be in cyclized form, cf. formula V, and can be employed as such in the process according to the invention. In the present case, compounds of the general formula V are also counted among those of the general formula III: 
where R methyl, ethyl, propyl or butyl, and
x=0, 1 or 2.
It is known that such a ring is opened on hydrolysis or alcoholysis and the corresponding aminoalkylalkoxy-silane or -silanol is obtained.
Compounds of the general formula IV can likewise be in cyclic or bicylic form and can be employed as such as in the process according to the invention.
In general, the process according to the invention is carried out by mixing amino silanes of the general formula III and IV, hydrolyzing them together and removing the resulting hydrolysis alcohols by distillation. Mixing of the alkoxy silanes can be carried out in a temperature range between the solidifying point and boiling point of the silanes employed. Generally, water is added in excess to the silane mixture for carrying out the hydrolysis.
The concentration of the silanes in the aqueous solution is suitably adjusted to a value of  less than 60% strength by weight, preferably  less than 50% strength by weight, particularly preferably is 0.01 to 40% by weight, and especially preferably 0.5 to 40% by weight. Deviation from these parameters can cause gel formation or severe clouding. Alcohol is formed on hydrolysis the alkoxy silanes.
In general, the hydrolysis can be carried out at a temperature in the range from 0 to 100xc2x0 C. The hydrolysis is preferably carried out at a temperature of  less than 100xc2x0 C., particularly preferably at  less than 90xc2x0 C., and especially preferably at  less than 60xc2x0 C. Generally, good thorough mixing is provided here, for example by stirring.
In the process according to the invention, the hydrolysis is suitably carried out at a pH in the range from 4 to 12. An acid or base can furthermore be added to the silane mixture or silane mixture/water system or the already hydrolyzed system to establish the pH.
Preferably, at least one Brxc3x6nsted acid is added in the process according to the invention. If necessary, a Brxc3x6nsted base can also be added, for example potassium hydroxide solution, sodium hydroxide solution and ammonia or amines, to name only a few. Hydrochloric acid, sulfuric acid, nitric acid, perchloric acid, formic acid, acetic acid and/or propionic acid are particularly preferred as the acid.
In the process according to the invention, the concentration of hydrolysis alcohol is furthermore lowered by distillation, the distillation preferably being carried out at a temperature of  less than 90xc2x0 C., particularly preferably at  less than 60xc2x0 C., and suitably under reduced pressure.
The distillation can advantageously be carried out via a distillation column and can be continued until no further alcohol can be detected at the top of the column, the desired product, which can optionally be worked up further, being obtained at the bottom. If clouding substances should occur, these can be removed from the product by means of filtration, sedimentation, centrifugation or similar standard processes.
The composition according to the invention can be applied from concentrated solution or a solution diluted with water. In the case of dilution with water, the storage stability of the composition diluted in this way can be improved by addition of acid. The pH of the diluted composition is suitably adjusted to a value of  less than 9.
The products obtained according to the invention have the advantage in particular that they are water-soluble, can be mixed with water spontaneously in all proportions, comprise a high content of bis(trihydroxysilylalkyl)amine and siloxanes derived therefrom, and are essentially alcohol-free.
Compositions according to the invention are furthermore used in an outstanding manner as water-soluble adhesion promoters, as a constituent in coating systems and in anticorrosion compositions, in particular in the coating of metal, for the biocidal treatment of surfaces, the treatment of wood, for electro-photographic toners, as a constituent in aminosilicone fluids, as a constituent in epoxy resins, phenolic resins, unsaturated polyester resins (UP resins) and acrylic resins, as a constituent in organically modified glasses, for pharmaceutical and cosmetic products, for the modification of surfaces of glass and minerals and glass fiber and mineral fiber surfaces, including glass beads, glass fabric and construction glass fabric, to name only a few examples, for wastewater treatment, for the treatment of pigments, as a constituent in the preparation of catalysts, as a flocculating agent, as a constituent in paints and coatings, in the preparation of artificial stone, for increasing the strength of plate glass, hollow glass and laminated glass, and as an adhesion promoter for crosslinking polymers, in particular acrylic compounds, on glass and other substrates. Accordingly, an important use of the inventive composition is a process for coating a surface comprising applying the inventive composition to the surface to be coated.